The present invention pertains to mobile telecommunications and more particularly to forward link power reduction methodology in soft handoff environments.
Mobile telecommunication systems include wireless links between mobile stations, which may be mobile telephones, pagers, computers, etc., and a base station of the mobile telecommunication system. Since these links are wireless, the links are susceptible to noise and interference with other signals. The signals received at the mobile station or at the base station (BS) may fade due to errors in the RF links or legs coupling the base station to the mobile unit. That is, the data signals received by the mobile station may become much more attenuated than the surrounding noise and other interference.
The quality of wireless telecommunication is often measured by the ability of the mobile unit to receive accurate and clear data from the base station. As errors are detected by the mobile unit, the base station may increase the transmission power on the leg which couples the base station and the mobile unit. When greater power is used on a RF link or leg, the power increase causes interference for other links or legs coupling the base station to other mobile units and with other links from other base stations coupling to the mobile unit in a soft hand off configuration.
When one of the legs between the mobile unit and a base station becomes weak, for example, a hill might interfere with line-of-sight transmission, typical base station equipment tends to rapidly drive up the weak leg or link to full power. This creates several problems. The first being that since the base station has a finite amount of power using excessive power in any one link will necessarily limit the power available for links with other mobile units. Second, excessive use of power by base station creates more RF interference for other mobile units in the area.
One solution to this problem has been to eliminate weak legs coupling base stations to the mobile unit. However, completely eliminating weak legs increases RF losses, since current weak legs may be future strong legs that maintain a call when the mobile unit drives over a hill, for example. That is the previously strong base station leg becomes the weak one and the previously weak base station leg becomes the good one and thereby saves and maintains the call.
Accordingly, it would be highly desirable to have a power reduction method which limits the effects of weak RF transmission links (or legs) with mobile units.